Obligatory reference to the Rosetta Code site which shows a good number of popular and less known problems with solutions in many programming languages.

https://rosettacode.org/wiki/Rosetta_Code

Edit: it seems the "more..." label down the 1st list to see all examples is broken. To explore the full list use this link instead:

https://rosettacode.org/wiki/Category:Solutions_by_Programmi...